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POGetting class field names and table column names from NHibernate metadata
 

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  1. POGetting class field names and table column names from NHibernate metadata
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    <p><strong>Background</strong></p> <p>I am using a legacy database with all kinds of ugly corners. One bit is auditing. There is a table listing tablename/field combinations of fields that should have an audit trail. For example, if there is a row that has "WORKORDER" for the table name and "STATUS" for the fieldname, then I need to add row(s) to the auditing table whenever the Workorder.Status property changes in the application. I know the approach: NH events or interceptors, but I've got an issue to figure out before I get to that stage.</p> <p><strong>Question</strong></p> <p>What I need to know is how to get a list of key/value pairs for a single persistent class containing (a) the database field name and (b) the associated property name in the class. So for my example, I have a class called Workorder associated with a table called (no surprise) WORKORDER. I have a property on that Workorder class called CurrentStatus. The matching property in the WORKORDER table is STATUS. Notice the mismatch between the property name and table column name? I need to know the property name to access the before and after data for the audit. But I also need to know the backing column name so that I can query the stupid legacy "AuditTheseColumns" table.</p> <p><strong>What I've tried</strong></p> <p>in my application I change the Workorder.CurrentStatus from "TS" to "IP". I look in my audit tracking table and see that the WORKORDER.STATUS column is tracked. So after calling Session.SaveOrUpdate(workorder), I need to find the Workorder property associated with the STATUS column and do a Session.Save(auditRecord) telling it the old ("TS") and new ("IP") values.</p> <p>As far as I can tell, you can get information about the class:</p> <pre><code> var fieldNames = new List&lt;string&gt;(); IClassMetadata classMetadata = SessionFactory(Resources.CityworksDatasource).GetClassMetadata(typeof(T)); int propertyCount = 0; foreach (IType propertyType in classMetadata.PropertyTypes) { if (propertyType.IsComponentType) { var cp = (ComponentType)propertyType; foreach (string propertyName in cp.PropertyNames) { fieldNames.Add(propertyName); } } else if(!propertyType.IsCollectionType) { fieldNames.Add(classMetadata.PropertyNames[propertyCount + 1]); } propertyCount++; } </code></pre> <p>And information about the table:</p> <pre><code> var columnNames = new List&lt;string&gt;(); PersistentClass mappingMeta = ConfigureCityworks().GetClassMapping(typeof(T)); foreach (Property property in mappingMeta.PropertyIterator) { foreach (Column selectable in property.ColumnIterator) { if (columnNames.Contains(selectable.Name)) continue; columnNames.Add(selectable.Name); } } </code></pre> <p>But not at the same time. Any ideas? I'm at a loss where to look next.</p>
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    1. COThis is not directly related to your question but it might be an idea - why don't you audit changes on object level instead on database? End users are dealing with .NET object in the UI level and because .NET data objects are not just 1:1 reflection of database objects (tables, views...) it's perhaps more accurate to audit events on .NET objects instead on database ones. What do you think?
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    2. COIf it were up to me I'd definitely be looking at that type of approach. Unfortunately I'm working with a database that sits behind a well established product and I cannot bypass their approach to auditing. So yes, I wish! But alas, not a viable approach for this project.
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    3. COFor me; I decided to use constants for storing the table names and key column name; then I use the constant in the nhibernate mapping files and raw tsql
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